Seismic Retrofit of Flared Reinforced Concrete Columns in Multispan Viaduct: From Research to Field Implementation

Following the failure of the flared column in the Mission Gothic Overpass during the Northridge Earthquake, a multiphase study of flared bridge columns in northern Nevada was undertaken. The study, the field implementation, and a cost-benefit analysis for a 16-span viaduct are summarized. The study included analytical evaluation of the piers in addition to quasistatic and shake table testing of large-scale as-built and retrofitted columns. The jacket material included steel, glass-fiber composites, and carbon-fiber composites. Results showed that shear retrofit provided sufficient displacement ductility capacity even though the confinement requirements were not met. All three jacket materials were found to be satisfactory. Because the space under the bridge was used for offices and garages and because the working space around many of the columns was limited, composite fabrics were selected for field implementation. Because the columns were flared and nonprismatic, a continuous wrap could not have been applied efficiently. A new method of composite installation was devised in the course of research and was used in the field. As a result of the research, less than one-third of the columns were found to be in need of retrofit. The cost-benefit analysis of the selected retrofit indicated a 64% saving over the cost of conventional column retrofit.